1. Field of the Invention
The present invention relates to a spray apparatus and method for spraying a crop or the like with an agricultural liquid spray and, more particularly, to a mobile spray apparatus adapted for spraying trees and other plants with, for instance, insecticides, herbicides, fungicides, etc., along their entire height.
2. Description of the Prior Art
It is well known to apply various chemical sprays to agricultural and horticultural crops, such as insecticides and fungicides, in order to protect the crops from diseases, insects, and the like. It is also well known to apply such chemical sprays with various spraying apparatuses which, for example, forcibly pass an airborne spray across and through the crop for maximizing the spray coverage on the crop of the spray apparatus.
For instance, U.S. Pat. No. 5,028,002 issued to Whitford on Jul. 2, 1991 discloses a cross-flow spraying assembly in which a fan creates an airstream with a spray liquid being injected in the airstream for spraying a crop. The airborne spray is passed by the airstream across the crop. The assembly includes a discharge hood located on the wheeled vehicle for spraying the liquid outwardly with respect thereto, and the assembly also includes a suction hood located on the other side of the crop, such that the crop is located between the discharge hood and the suction hood, with the suction hood being adapted to recuperate the spray liquid that passes through the crop such that the recuperated spray liquid may be recirculated towards the discharge hood. In this system, suction and pressure are both used, namely on opposite sides of the crop.
U.S. Pat. No. 5,214,876 issued to Sukup on Jun. 1, 1993 discloses an implement for the removal of insects or the like from upstanding plants. The implement is generally used for removing insects or the like from plants using a pressurized stream of air. In Sukup, the circulation of the airflow is reversed with respect to the aforementioned Whitford Patent, in that the system's exhaust directs the airstream through the plant row and towards the motor vehicle and, more particularly, towards a fan intake of the implement, whereby a portion of the exhaust airflow re-enters the intake airflow thereby forming a closed circuit airflow. Also, pesticides or herbicides may be introduced in the closed-circuit airflow for spraying the plants while permitting recirculation of the sprayed liquid which passes through the plants.
Spraying is necessary in order to protect trees and bushes from insect pests or diseases. It is also a preferred means for applying some fertilizers, growth regulators as well as other treatment products.
The typical sprayer is of the blower type and uses a pump serving to convey the spray material to a fan where it is discharged into an air stream in small droplets using a number of nozzles. The air stream assists in breaking up the liquid into small particles. The air stream also acts as a diluent to prevent the small particles from coalescing and carries the fine droplets to the plant from a distance thereof. The coverage is also improved as turbulence in the air is created and the foliage is shaken. In some implementations, the high-speed airstream is also used to atomize the liquid.
In orchards, spraying is conventionally made by a tractor-drawn sprayer including a large tank and a large fan blowing air outwardly and upwardly, creating a large, almost 240-degree radial air blast. This radial pattern results in that the part of the spray missing the target gets over the canopy where it is carried away by stronger winds.
Some trees, for instance apple trees, must be sprayed early in the spring, that is when the trees are devoid of leaves thereby resulting in that most of the treatment product is lost in the environment. Recovery of the spray treatment product could reduce pollution and treatment products costs. The loss of pesticide also results in more time needed for transport and replenishing of tank with water and chemicals. In a context of integrated pest management, amounts of pesticide may be reduced by a better timing of spray treatments in order to optimize their effects. Also, extended possibilities to treat despite non ideal weather conditions could increase treatment efficiency which is related to the timing of the application of the spray treatment. Also, without protection against the wind, the sprayed treatment has more chance to miss the target and cause more drift.
Presently, tower sprayers use ducts and deflectors to redirect the upward part of the air blast in a more horizontal air stream, thus reducing drift at top the trees.
U.S. Pat. No. 5,383,599 issued on Jan. 24, 1995 to Zur uses an inflatable sleeve to redirect radial air blast in an air curtain more parallel to the tree. Cross-flow fans which generate a uniform air curtain are also commercially available.
It is known that smaller droplets result in a better coverage but they are also more prone to drift. The trend in Europe over the last 20 years, and presently in the United States, is to have higher density plantings of dwarf trees, which explains the growing popularity of tunnel sprayers which permit for the use of smaller droplets. In typical tunnel sprayers (such as in Keathley's U.S. Pat. No. 4,893,755 issued on Jan. 16, 1990), the plant is confined by a canopy and the treatment agent is sprayed in this confined zone.
Blowers are also used to circulate air in the hood in order to carry the product to be applied to the central parts of the plants. The recovery is done by impaction or deposition on inner walls and bavettes installed at the bottom of the walls recover liquid which is then pumped back into the reservoir.
The large structure of tunnel sprayers results in that at least one wheel is required on the other side of the plants, thereby reducing the speed of operation.
Another type of tunnel sprayer developed by Hulls (see U.S. Pat. No. 5,662,267 issued on Sep. 2, 1997) uses an atmosphere over saturated with droplets between 30 and 60 microns and the agent is applied to the plants through the process of condensation and coagulation.
However in these systems, the surface of recovery is limited to the walls of the tunnel and bavettes installed at their lower ends, and the mist which remains in the canopy is free to drift after the tunnel has passed over.
Also, in many tunnel sprayers, the droplets' velocity resulting from the air blast makes it difficult to confine the sprayed product.
The principle of drift removal was disclosed by Owanezyk (U.S. Pat. No. 4,865,628 issued on Sep. 12, 1989) who moved a hood over the vineyard with a fan pulling the drift from the hood to a de-mister and an activated charcoal container. This system however did not enjoy the benefits of air-assisted spraying devices for penetrating the canopy and the suction effect rapidly weakens at a distance from the inlet, whereby this principle may hardly be applied to trees of high dimensions.
Recirculating sprayers having a cross-flow configuration (see Withford's U.S. Pat. No. 5,028,002 and Sukup's U.S. Pat. No. 5,214,876, both mentioned hereinabove) blow air charged with liquid treatment through a crop with a suction hood being disposed on the other side to receive part of the overspray which condenses in conduits or recirculates in ventilation.
The portion of the treatment product recovered or recirculated is however limited to the part captured by the suction hood and the inner walls of ducts. Since only the vacuumed air is treated, the rest is lost. Under the effect of entrained air, it becomes impossible to cover all blown air and have a closed circuit. Furthermore, under wind and travel effects, the droplet charged air stream may become deviated from the suction hood, especially for large plants like fruit trees. It becomes therefore necessary to add to the receiving surface of the inlet suction hood.
An example of a passive collecting device is found in Australian Patent Specification No. 50424/79 (U.S. Pat. No. 4,168,798 issued on Sep. 25, 1979 to Moore et al.), wherein "solid stream" spray nozzles direct a spray to fibrous collector panels from which the liquid is recirculated. In the case of an air stream charged with droplets, such a device should let airflow through easily while condensing excess spray treatment. A plain absorbing surface would deviate the air stream around and excess spray treatment would get lost as well.